The meat-eating shark is one of the most feared creatures in the ocean. Now, the shark has reason to be afraid. Scientists have recently reported that the number of sharks in the North Atlantic Ocean and Gulf of Mexico has declined by half in the past 15 years.
About 370 species, or kinds, of sharks live in the waters around the world. The researchers found that populations of some of the best-known sharks, including hammerheads and great whites, have been affected. The hammerhead suffered the steepest drop--an 89 percent decrease. The number of great white sharks declined by 79 percent.
According to scientists, the dramatic drop in shark populations is due to over-fishing. The shark population is also threatened because sharks develop slowly and do not reproduce as quickly as other types of fish.
What Can Be Done?
Many sharks are accidentally killed as bycatch, or unwanted catch, in nets meant for tuna and swordfish. Some scientists think that tighter laws on fishing could protect sharks. For example, some sharks migrate, or move to another place, along set paths at certain times of the year. Some scientists say that preventing fishing during those times might help protect sharks from being accidentally killed.
Another risk to sharks are the people who kill them for their fins, which are used to make shark-fin soup. The United States prohibits that practice.
Altering the Food Chain
The decline in the shark population has scientists worried. All plants and animals in the ocean depend on one another for food. The link between them is called the food chain (see sidebar).
Sharks are predators at the top of the food chain. A predator is an animal that survives by eating other animals. Sharks hunt, or prey upon, other animals such as seals and tuna. Seals and tuna eat smaller fish. Those smaller fish feed on tiny fish and ocean plants.
"Sharks are adapted to being the predators, not the prey," said one scientist. Scientists say that if sharks are wiped out, it would negatively impact other marine life in the food chain.
Ocean Food Chain
The food chain links plants and animals together. They depend on one another for food. The ocean food chain begins with sea plants called phytoplankton. Tiny animals called zooplankton eat the phytoplankton. A small fish, such as a herring, eats the zooplankton. A bigger fish, such as a tuna, eats the herring. A predator, such as a shark, eats the tuna.
What do you think should be done to protect sharks? Discuss in class. Then let us know in the Write On section of http://www.weekly reader.com/kids/grade4.